bcachefs: don't expose "read_only" as a mount option

When "read_only" is exposed as a mount option, it is redundant with the
standard option "ro" and gives users multiple ways to specify that a
bcachefs filesystem should be mounted read-only. This presents the risk
of having inconsistent options specified.

This can be seen when remounting a read-only filesystem in read-write
mode, using mount(8) from util-linux. Because mount(8) parses the
existing mount options from `/proc/mounts` and applies them when
remounting, it can end up applying both "read_only" and "rw":

$ mount img -o ro /mnt
$ strace mount -o remount,rw /mnt
...
fsconfig(4, FSCONFIG_SET_FLAG, "read_only", NULL, 0) = 0
fsconfig(4, FSCONFIG_SET_FLAG, "rw", NULL, 0) = 0
...

Making "read_only" no longer a mount option means this edge case cannot
occur.

Fixes: 62719cf33c3a ("bcachefs: Fix nochanges/read_only interaction")
Signed-off-by: Thomas Bertschinger <tahbertschinger@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

diff --git a/fs/bcachefs/opts.h b/fs/bcachefs/opts.h
index b197ec90d4cb0295b4311c66293d8bad189cbc06..c9da6267894b6dbfef8864c38e3322fa0abbeafc 100644 (file)
--- a/fs/bcachefs/opts.h
+++ b/fs/bcachefs/opts.h
@@ -406,7 +406,7 @@ enum fsck_err_opts {
          BCH2_NO_SB_OPT,               BCH_SB_SECTOR,                  \
          "offset",     "Sector offset of superblock")                  \
        x(read_only,                    u8,                             \
-         OPT_FS|OPT_MOUNT,                                             \
+         OPT_FS,                                                       \
          OPT_BOOL(),                                                   \
          BCH2_NO_SB_OPT,               false,                          \
          NULL,         NULL)                                           \